Astrocytes are thought to play an important role in regulating the composition of the extracellular environment in the nervous system. Both anatomical and physiological investigations have localized various ion channels and neurotransmitter uptake systems to astrocytic processes within the neuropil. Computer modeling offers one avenue for investigating the capacity of astrocytic processes to affect the extracellular milieu surrounding neuronal cell bodies, axons and dendrites. In order to construct such models, accurate measurements of surface area and volume of individual astrocytes will be necessary. Golgi-impregnation of astrocytes indicates that each astrocyte possesses an extensive array of fine processes which greatly increase surface area but which cannot be resolved by the light microscope. In the present collaboration, we are using tomographic reconstructions to obtain surface area and volume measurements of Golgi-impregnated astrocytes. In some cases, entire ast rocytes will be reconstructed using serial tomography. This work is being carried out jointly at the NCMIR using the IVEM and at the National Institute for Physiological Sciences in Okasaki, Japan, using the 1meV electron microscope. We have been participating in a scientific exchange program in order to implement the routines for performing tomographic reconstructions developed at NCMIR in Okasaki. Currently, all of the software has been implemented.